The Cincinnati Bengals have had a season to remember, winning their first eight games and finishing 12-4, their best record since 1988. But in a wild-card playoff game on Saturday night, they will be underdogs at home to the Pittsburgh Steelers, whom they beat for the A.F.C. North crown. The reason is the absence of their starting quarterback, Andy Dalton, one of the league’s top passers this season.

Dalton fractured the thumb on his throwing hand in a loss to the Steelers in Week 14. Although his cast has been removed, he has been ruled inactive for Saturday’s game, which means the backup A. J. McCarron will start.

That Dalton would be considered so vital to the team at this point in the season would have been a surprise to many Bengals fans in the off-season. Confidence in Dalton was low, with some calling for him to be benched. He was even booed at a celebrity softball game in July.

Dalton’s strong season has silenced most of his doubters, but his injury means at least a minority think sticking with a healthy McCarron, should the Bengals advance, might be a wiser play.

For Bengals fans hungry for playoff success, the quarterback question is front and center. Here is a look at the team’s top two quarterbacks.

The Basics

DALTON Age 28, a second-round pick out of Texas Christian University, where he was a four-year starter and led the team to a perfect record in his senior year, 2010.

MCCARRON Age 25, a fifth-round pick out of Alabama, where he was a two-time national champion.

N.F.L. History

DALTON A five-season starter who produced a winning record in each season. That is the only five-year string of winning records in team history. His numbers have steadily improved, and this season he broke into the ranks of the quarterback elite.

MCCARRON Did not get in a game in 2014, his rookie season.

2015

DALTON 10-2 this season before being hurt in the Steelers loss. Only defeats came against playoff teams, the Cardinals and the Texans.

MCCARRON Completed the Steelers loss, then was 2-1 to finish the season, including a loss at Denver.

Accuracy

DALTON Completed a career-high 66 percent of his passes this season, with a career-low 1.8 percent interception rate.

DALTON Has led the Bengals to five straight playoffs but has fared poorly in the postseason, going 0-4 with an ugly 3.9 adjusted yards per attempt.

MCCARRON Will be making his playoff debut.

On paper, McCarron is promising, and looking at backups around the N.F.L., the Bengals could do a lot worse. He has shown a knack for avoiding interceptions, although he has yet to show Dalton’s ability to go deep.

Still, after Dalton’s fine season, it is hard to conclude anything but that the Bengals will be at a significant disadvantage behind the unseasoned McCarron. Most Bengals fans seem to have come around on Dalton; certainly, there was no celebration at his injury.

The uneasiness that some have about Dalton is chiefly emotional, rather than statistical. For a fan base that has not had a playoff win since 1990, losing four in a row under Dalton has left a psychic scar, and words of consolation like “small sample size” ring hollow. McCarron’s success in college is also fresh in the memory, and the notion lingers that he is magic in big games, like the college national championship.

Should McCarron deliver a long-awaited playoff win, he will no doubt be lionized in Cincinnati, and the decision on who will start at New England next week would become very interesting.

A version of this article appears in print on , Section D, Page 2 of the New York edition with the headline: Bengals’ Hopes Could Ride on a Thumb. Order Reprints | Today’s Paper | Subscribe